Multiple beam inspection apparatus and method

Abstract

Disclosed is an optical inspection system for inspecting the surface of a substrate. The optical inspection system includes a light source for emitting an incident light beam along an optical axis and a first set of optical elements arranged for separating the incident light beam into a plurality of light beams, directing the plurality of light beams to intersect with the surface of the substrate, and focusing the plurality of light beams to a plurality of scanning spots on the surface of the substrate. The inspection system further includes a light detector arrangement including individual light detectors that correspond to individual ones of a plurality of reflected or transmitted light beams caused by the intersection of the plurality of light beams with the surface of the substrate. The light detectors are arranged for sensing the light intensity of either the reflected or transmitted light.

1. An optical inspection system for inspecting a surface of a sample for defects, comprising:
 a stage for placing the sample thereon; 
 a light source for emitting an incident light beam along an optical axis; 
 an optical system for receiving the incident light beam and including a first set of optical components for separating the incident light beam into a plurality of individual light beams, that are incident on a plurality of scanning spots at different locations on the surface of the sample and 
 a control system for moving the stage relative to the optical axis in a first direction, 
 wherein the first set of optical components are further arranged to cause the individual light beams and their corresponding scanning spots to be deflected along individual scan paths in a second direction that differs from the first direction, the individual scan paths being offset from each other in the first direction so that a scan of a same location of the first direction by the different scanning spots are offset and isolated from each other. 
 
   
   
     2. The optical inspection system as recited in  claim 1 , wherein the first direction is perpendicular to the second direction. 
   
   
     3. The optical inspection system as recited in  claim 1 , further comprising a light detector arrangement including individual light detectors that correspond to individual ones of a plurality of reflected and/or transmitted light beams caused by the intersection of the individual light beams with the surface of the sample, the light detectors being arranged for sensing either the reflected or transmitted light. 
   
   
     4. The optical inspection system as recited in  claim 3 , wherein the individual light detectors correspond to individual ones of a plurality of reflected and transmitted light beams caused by the intersection of the plurality of light beams with the surface of the reticle mask, or semiconductor wafer, the individual light detectors being arranged for sensing characteristics of the reflected and-transmitted light that can be used for analysis associated with the surface of the sample. 
   
   
     5. The optical inspection system as recited in  claim 3 , wherein individual light detectors correspond to individual ones of a plurality of reflected light beams caused by the intersection of the plurality of light beams with the surface of the sample, the individual light detectors being arranged for sensing characteristics of the reflected light that can be used for defect analysis associated with the surface of the sample. 
   
   
     6. The optical inspection system as recited in  claim 3 , wherein the individual light detectors correspond to individual ones of a plurality of transmitted light beams caused by the intersection of the individual light beams with the surface of the sample, the individual light detectors being arranged for sensing characteristics of the transmitted light so as to perform defect analysis associated with the surface of the sample. 
   
   
     7. The optical inspection system as recited in  claim 3 , wherein the first set of optical components are further arranged for separating the incident light beam into the individual beams so that they are spatially distinct light beams that are staggered relative to one another. 
   
   
     8. The optical inspection system as recited in  claim 7 , further comprising a second set of optical elements adapted for collecting a plurality of reflected light beams and/or a plurality of transmitted light beams caused by the intersection of the individual light beams with the surface of the sample, wherein the second set of optical elements is arranged for collecting the plurality of spatially distinct light beams, which have intersected with the surface of the sample, and for directing individual ones of the collected light beams to the individual light detectors of the light detector arrangement. 
   
   
     9. The optical inspection system as recited in  claim 3  wherein the first set of optical elements comprises a beam deflector disposed along the optical axis, the beam deflector being arranged for deflecting the light beam such that the individual light beams are caused to sweep across the surface of the sample in substantially the second direction from a first point to a second point. 
   
   
     10. The optical inspection system as recited in  claim 9 , wherein the beam deflector comprises an acousto-optic device for causing the light beam to be deflected over a relatively small angle, the angle being at least one of the factors for determining a length of each of the individual scan paths of each of the individual light beams. 
   
   
     11. The optical inspection system as recited in  claim 3 , wherein the first set of optical elements comprises a beam separator disposed along the optical axis, the beam separator being arranged for separating the light beam into the individual light beams. 
   
   
     12. The optical inspection system as recited in  claim 11 , wherein the beam separator is a diffraction grating. 
   
   
     13. The optical inspection system as recited in  claim 12 , wherein the diffraction grating is arranged for separating the light beam into the individual light beams so that such individual light beams takes the form of a plurality of spatially distinct light beams, which when focused on the surface of the sample produce the plurality of scanning spots so that they are offset and staggered relative to one another in the first direction and in the second direction, and which cause a portion of a scan length of the scanning spots to overlap one another in the first direction. 
   
   
     14. The optical inspection system as recited in  claim 13 , wherein the diffraction grating has a grating spacing and a grating rotation about the optical axis, and wherein each of the scanning spots has a specified overlap and separation that is controlled by the grating spacing and the grating rotation. 
   
   
     15. The optical inspection system as recited in  claim 12 , wherein the diffraction grating is selected from one of a transmission type grating or a reflective type grating. 
   
   
     16. The optical inspection system as recited in  claim 15 , wherein the transmission type grating is selected from one of a phase grating or an amplitude grating. 
   
   
     17. The optical inspection system as recited in  claim 1 , wherein the control system is further arranged to move the stage-so that it transports the sample along the first direction. 
   
   
     18. The optical inspection system as recited in  claim 1 , wherein the first set of optical components are further arranged to partially overlap the scan paths of the individual light beams in the second direction so that the individual light beams and their corresponding scan paths together scan a scanning swath in the second direction without missing areas between such individual scan paths in the second direction. 
   
   
     19. The optical inspection system as recited in  claim 1 , wherein the control system is further arranged to move the stage relative to the optical axis in at least two linear directions within an inspection plane.